Heat exchanger

ABSTRACT

A corrugated heat exchanging fin element for use with a heat exchanger. The fin element has formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction. Each louver is depressed at the trailing side of the louver as viewed in the direction of feeding of a strip material for the formation of the louvers so that the stresses produced in the material of the louvers at the time of manufacture is removed to enable the fin element to be free from arcuate bend from which the fin element otherwise suffers.

United States Patent [191 Yamaguchi et a1.

[54] HEAT EXCHANGER [75] Inventors: Terumoto Yamaguchi; Yoshinao Amano, both of Anjo-shi, Japan [73] Assignees Nippondenso Co., Ltd., Kariya-shi,

Japan 22 Filed: '0ct.27, 1971 [21] Appl.No.: 193,117

[30] Foreign Application Priority Data 51 Apr. 3, 1973 [56] References Cited UNITED STATES PATENTS 3,433,044 3/1969 Rhodes et a1 ..72/186 Primary Examiner-Albert W. Davis, Jr. AttorneyCushman, Darby 8:. Cu-shman [5 7] ABSTRACT A corrugated heat exchanging fin element for use with a heat exchanger. The fin element has formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define; apertures opened in substantially the same direction. Each louver is depressed at the trailing side of the louver as viewed in the direction of feeding of a strip material for the formation of the louvers so that the stresses produced in the material of the louvers at the timelof manufacture is removed to enable the fin element to be free from arcuate bend from which the fin element otherwise suffers.

7 Claims, 18 Drawing Figures PATENTEUAPRS I975 3.724.538

SHEETSUFS INVENTORS yos/w/vflo fl/msm o 7220/1070 yam/96 z/c/// BACKGROUND OF INVENTION 1. Field of Invention The present invention relates generally to a heat exchanger and, more particularly, to a corrugated heat exchange fin structure having formed therein rows of louvers directed at an angle with respect to the flow of a coolant and cut to define apertures opened substantially in the same direction.

2. Description of Prior Art In general, a heat exchanger comprises conduits and corrugated heat exchanging fins secured thereto by means of soldering. Louvers are formed in the heat exchanging fins so as to improve the heat exchange efficiency. There are many types in the arrangement or design of louvers. One type of louver arrangement is such that louvers are directed at an angle with respect to the flow of a coolant such as air and are cut to define apertures opened in substantially the same direction. Heat exchanging fin elements having louvers of this type are known to provide a large heat exchange efficiency and a decreased pressure drop of the coolant across the elements. However, this type of louver design has not been employed in mass-production. This is because the mentioned type of louver designhas an inherent disadvantage that a fin element having formed therein a series of louvers of the above-mentioned type of louver design is caused to have an arcuately, curved or bent configuration with a disadvantage result that it is difficult to assemble and secure the fin element and conduits together to form a completed heat exchanger part.

SUMMARY OF INVENTION It is an object of the present invention to provide an improved heat exchanging fin structure which is free from the above-discussed disadvantage and difficulty.

It is another object of the present invention to provide a heat exchanger which has heat exchanging fin elements of the class specified in the preceding paragraph.

It is a further object of the present invention to provide a novel method of producing heat exchanging fin elements of the class specified in the above.

According to one aspect of the invention, there is provided a corrugated heat exchanging fin element for use with a heat exchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a strip material for the formation of the fin element so that the stress produced in the material of the louver is at least partially removed.

According to another aspect of the present invention, there is provided a heat exchanger including conduits for a heat exchanging fluid and corrugated heat exchanging fin elements secured to the conduits, each of said fin elements having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a metal strip for the formation of the fin element so that the stress produced in the material of the louver is at least partially removed.

According to a further aspect of the present invention, there is provided a method of manufacturing a corrugatedheat exchanging fin element for use with a heat exchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, said method comprising the steps of feeding a metal strip into the nip of a pair of toothed roller dies having at least a row of louver forming blades formed on each of the teeth on the roller dies to cause the metal strip to be corrugated and formed with rows of louvers by said teeth and louver forming blades for forming an unfinished fin element, then feeding the latter into the nip of another pair of toothed rollers having at least a row of louver deforming portion on each of the teeth of the rollers to cause one of the leading and trailing sides of each of the louvers to be deformed by said louver deforming portions whereby the stress produced in said trailing side of each louver at the time the same is formed is at least partially removed by the deformation. 7

Other objects, features and advantages of the present invention will be made apparent by the following description with reference to the accompanying drawings. 7

DESCRIPTION OF DRAWINGS FIG. 6 is a diagrammatical illustration of a heat exchanging fin element of the present invention before the element is secured to heat exchanger conduits;

FIGS. 7 through 11C diagrammatically illustrate the physical mechanism which causes the prior art heat exchanging fin element to be arcuately bent;

FIG. 12 diagrammatically illustrates the process of forming a heat exchanging fin element according to the present invention;

FIG. 13 is a fragmentary sectional view of roller dies for forming the fin element shown in FIG. 12; and

FIG. 14 is a fragmentary sectional view of roller dies for pressing and deforming louvers formed on the fin element shown in FIGS. 12 and 13.

DESCRIPTION OF A PREFERRED EMBODIMENT In order that the basic concept of the present invention may be clearly understood, a description will be made hereunder with respect to the prior art shown in FIGS. 1 through 4 and 7 through 1 1C of the drawings.

FIG. 1 illustrates a part of typical prior art heat exchanger comprising conduits 1 for a heat exchanging fluid and corrugated heat exchanging fins 2 secured to the conduits 1 by any conventional securing means such as soldering. As shown in FIG. 2, each fin 2 is corrugated or folded to provide a plurality of heat radiation surfaces 2a in each of which a series of louvers 3 are formed to improve the heat exchange efficien cy. FIG. 3 illustrates an example of most efficient louver arrangement or design in which the louvers 3 in all of the heat radiation surfaces 2a are directed at an angle with respect to the flow of a coolant, such as air, indicated by an arrow A so that the louvers cooperate together to define openings or apertures 3a opened substantially in the same direction.

This type of louver design is known to provide a large heat exchange efficiency and a decreased pressure drop of the coolant across the heat exchanger. This type of louver design, however, has an inherent shortcoming that a heat exchanging fin 2 having formed therein louvers of this type of louver arrangement is caused to have an arcuately curved or bent configuration as shown in FIG. 4. It is very difficult and involves troublesome works tosecure such an arcuately bent fin element to conduits by means of soldering or the like. For this reason, the louver design of the type concerned is not employed in mass-production of heat exchanging fin elements in spite of the fact that the louver design per se is quite advantageous.

Extensive researches have been made on the disadvantageous arcuate bend, as shown in FIG. 4, of prior art heat exchanging fin element which is formed therein with louvers 3 of the above-discussed louver arrangement. A description will be made hereunder with respect to the physical mechanism of the arcuate bend of the prior art heat exchanging fin element. FIG. 7 is a diagrammatical fragmentary plan view of an unfolded prior art heat exchanging fin element 2 having formed therein louvers 3 of the above discussed design. It will 7 be seen that the louvers 3 in a surface or zone 2a are punched to project or extend in a direction substantially opposite to that in which the louvers 3 in adjacent zones 2a extend. This arrangement is required for a folded or corrugated heat exchanging fin element 2 to have louvers 3 of the above-discussed type of louver design, i.e., substantially parallel louvers in the folded and corrugated form of the fin element 2, as shown in FIG. 3. The zones 2a of the unfolded fin element 2 in which the louvers 3 are punched to extend in one direction are represented by X while the zones 2a in which the louvers3 are punched to extend in a substantially opposite direction are represented by Y. The zones of the unfolded fin element 2 corresponding to the convex bends or so-called mountains in corrugated condition are represented by Z while the zones corresponding to the concave bends or socalled valleys in corrugated condition are represented by Z. Assuming that a metal strip is fed in a direction indicated by an arrow K sothat the strip is formed into a corrugated heat exchanging fin element 2 having formed therein louvers 3 as will be described later in more detail, the zones X and Y are first brought into cutting engagement with louver forming dies at the sides B of the respective zones adjacent the valley zones 2', the sides B being termed hereafter as leading sides. On the other hand, the louver forming dies leave the zones X and Y at their sides 01 adjacent the mountain" zones Z, the sides a being termed hereafter as trailing sides.

FIGS. 10A through 10C diagrammatically illustrate the deformation of a single louver 3 in the zone X of a fin element as shown in FIG. 7, FIG. 10A being a diagrammatical plan view of a single louver 3 while FIGS. 10B and 10C are diagrammatical sectional views taken substantially along lines XB-XB and XC-XC in FIG. 10A, respectively. The broken lines 7 in FIGS. 10B and 10C represent the general plane of the fin element 2. From the consideration on the deformation of a single louver 3 in the zone X, it has been found that, as shown in FIG. 10B, the material of the louver 3 on the trailing side 01 thereof is deformed from the broken line position to the solid line position, the broken line position being taken by the material of the louver 3 immediately after the formation thereof. Similarly, the material of the louver 3 on the leading side B thereof is deformed as shown in FIG. 10C, i.e., from the broken line position to the solid line position, the broken line position being taken by the material of the louver on the leading side B immediately after the formation of the louver. Stated in other words, it has been found that the trailing side a of the louver 3 has produced therein a stress which tends to cause the material in this side to approach the general plane 7 of the fin element 2 while the leading side B has produced therein a stress which tends to cause the material in this side to move or deform away from the general plane 7 of the fin element 2. 7

FIGS. 11A through 11C are views similar to FIGS. 10A to 10C, respectively, but diagrammatically illustrate the deformation of a single louver 3 in a zone Y of the fin element 2. It will be seen in FIGS. 11B and 11C that the trailing side a of the louver 3 in the zone Y has produced therein a stress which tends to cause. the material in this side to approach the general plane 7 of the fin element 2 while the leading side B has produced therein a stress which tends to cause the material in this side to move or deform away from the general plane 7 of the fin element 2.

In FIGS. 10A and 11A, the marks @represent the stresses which act on the material in the direction upwardly from behind the surfaces of these figures while the marks Qrepresentthe stresses acting in the opposite direction, i.e., from above the surfaces of the drawings downwardly toward behind the surfaces.

FIG. 7 diagrammatically illustrates the stresses which cause a corrugated fin element 2 to be deformed in its entirety. Specifically, the mountain zones Z in one of the side edges 2c of the fin element 2 have produced therein the stressesGB which cause the material in the zones Z in this side edge to be deformed in a direction upwardly from behind the surface of FIG. 7 while the valley zones Z in the side edge 20 have produced therein the stresses 9 which cause the material in the zones Z in the side edge 20 to be deformed downwardly toward behind the surface of FIG. 7, as will be best seen in FIG. 8 which is a diagrammatical side elevational viewof the fin element 2 as taken substantially along line IIX-IIX in FIG. 7 and which diagrammatically illustrates by arrows the directions of deformations. On the other hand, the mountain" zones Z in the other side edge 2d of thejfin element 2 have produced therein the stresses 9 which cause the material in the zones Z in the side edge 2d to be deformed downwardly toward behind the surface of FIG. 7 while the valley zones Z in the side edge 2d have produced therein the stresses ZBwhich cause the material in the zones Z to be deformed upwardly from behind the surface of FIG. 7, as will be best seen in FIG. 9 which is a diagrammatical side elevational view of the fin element 2 as taken substantially along line IXIX in FIG. 7 and which diagrammatically illustrates by arrows the direction of deformations. Stated in other words, the deformation in the side edge 2c in its entirety is such as to narrow the pitch of the corrugation in the edge of the fin element 2 as shown in FIG. 8 while the deformation in the side edge 2d in its entirety is such as to widen the pitch of the corrugation in the edge 2d of the fin element 2 as shown in FIG. 9. This difference in the deformation between the side edges 26 and 2d is considered to cause the fin element 2 in its entirety to be arcuately curved or bent as shown in FIG. 4.

From the above consideration, the arcuate bend of a conventional fin element 2 of the class concerned is believed to be caused by the fact that the trailing sides or in the zones X and Y have produced therein the stresses which cause the louvers 3 in these zones to be deformed in directions toward the general plane 7 of the fin element 2. So as to remove these stresses, the inventors have thought of depressing the trailing sides a of the louvers 3 in the zones X and Y to positively deform the material in these sides toward the general plane 7 of the fin element 2.

FIG. 5 of the drawings illustrates in side elevation the shape of each louver 13 of a heat exchanging fin element 12 manufactured according to the above concept of the present invention. It will be understood that, since the trailing side a of each louver 13 is depressed, the stresses. produced in the material of the trailing sides a of the louvers 13- of the fin element 12 of the present invention are advantageously at least partially removed to enable the fin element 12 to be free from an arcuate bend, as shown in FIG. 6.

In stead of depressing the trailing sides a of the louvers 13, the leading sides B may be raised away from the general plane 7 of the fin element 12 so as to remove'the stresses produced in the material of the leading sides at the time the fin element 12 is formed with the louvers 13. This alternative work, however, is less practical because it is difficult to prepare a tool, i.e., roller dies for this purpose.

A process for manufacturing a heat exchanging fin element 12 according to the method of the present invention will be described hereunder with reference to FIGS. 12 through 14 of the drawings. A metal strip 11 is fed in a direction indicated by an arrow K, into the nip of a pair of toothed roller dies 21 and 21a which are rotated in opposite directions as indicated by arrows B and C, respectively, to form the strip 11 into an unfinished product 11a, as shown in FIG. 12. More specifically, the roller dies 21 and 21a have axially extending teeth 22 and 22a, respectively. Each tooth 22 on the roller die 21 has formed thereon a pair of axial rows of louver forming blades 23 while each tooth 22a on the other roller die 21a has similar rows of blades 23a, as shown in FIG. 13. The teeth 22 and 22a and the blades 23 and 23a cooperate together to form the metal strip 11 into a corrugated but unfinished fin element having rows of louvers 13 formed therein.

The unfinished product 11a is then advanced into the nip of another pair of louver pressing toothed rollers 25 and 25a having teeth 26 and 26a of substantially the same pitch as that of the teeth 22 and 22a of the roller dies 21 and 21a. Each tooth 26 of the roller 25 has a pair of rows of louver depressing portions 27 and 28 of involute profiles while each tooth 26a of the other roller 25a has a pair of rows of similar louver depressing portions 27a and 28a, as best seen in FIG.

14. The rollers 25 and 25a are also rotated in opposite directions B and C, respectively. When the rollers are so rotated, the louver depressing portions 27, 28, 27a and 28a on the rollers cooperate together to depress the trailing sides a of the louvers 13 on the unfinished fin element 11a for the described purpose to complete the process of the invention, i.e., to form a finished heat exchanging fin element 12. The teeth 26 and 260 are relieved as at 29 and 29a adjacent the louver depressing portions 27, 28, 27a and 28a so that the louvers 13 except their trailing sides a are not deformed by the teeth 26 and 26a.

The finished fin element 12 may, if required, be driven or advanced by a further pair of toothed advancing rollers 31 and 31a having teeth of the pitch which is substantially the same as that in the preceding pairs of rollers 21 and 21a and 25 and 250:. The portion ofthe fin element 12 advanced by the toothed rollers 31 and 31a may then be subjected to a braking action by a plate 33 which is in frictional sliding contact with the run of the fin element 12 and is resiliently urged against the latter by means of a resilient member such as a spring 34 supported from a machine frame M. The advancing rollers 31 and 31a cooperate with the braking plate 33 to narrow or reduce the pitch of the corrugation of the fin element 12 into a modified pitch which is suited for an intended application to heat exchanger conduits. Reference numerals 35a, 35b, 35c and 35d represent guides which support and guidethe runs of the metal strip 11, the unfinished product 11a and the finished product or heat exchanging fin element 12, respectively.

What is claimed is: V

1. A corrugated heat exchanging fin element for use with a heat exchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a strip material for the formation of the fin element so that the stress produced in the material of the louver is at least partially removed.

2. A corrugated heat exchanging fin element as defined in claim 1, wherein each. of said louvers is depressed at the trailing side thereof.

3. A heat exchanger including conduits for a'heat exchanging fluid and corrugated heat exchanging fin elements secured to the conduits, each of said fin elements having formed thereon therefrom at an angle with respect to the flow ofa coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a metal strip for the formation of the fin element sothat the stress produced in the material of the louver is at least partially removed.

4. A heat exchanger as defined in claim 3, wherein each of said louvers is depressed at the trailing side thereof.

5. A method of manufacturing a corrugated heat exchanging fin element for use with a heatexchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, said method comprising the steps of feeding a metal strip into the nip of a pair of toothed roller dies having at least a row of louver forming blades formed on each of the teeth on the roller dies to louvers extending cause the metal strip to be corrugated and formed with rows of louvers by said teeth and louver forming blades for forming an unfinished fin element, then feeding the latter into the nip of another pair of toothed rollers having at least a row of louver deforming portion on each of the teeth of the rollers to cause at one of the leading and trailing sides of each of the louvers to be deformed by said louver deforming portions whereby the stress produced in said trailing side of each louver at the time the same is formed is at least partially removed by the deformation.

6. A method as defined in claim 5, wherein the trailing side of each of said louvers is'depressed-by said louver deforming portions on said another pair of rollers.

7. A method as defined in claim 6, wherein, after the depression, the corrugated heat exchanging fin element is advanced into the nip of a further pair of toothed rollers by which said fin element is positively driven and advanced to a braking means which is in frictional sliding contact with the run of the fin element to narrow the pitch of the corrugation of the fin element by the braking action of said braking means. 

1. A corrugated heat exchanging fin element for use with a heat exchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a strip material for the formation of the fin element so that the stress produced in the material of the louver is at least partially removed.
 2. A corrugated heat exchanging fin element as defined in claim 1, wherein each of said louvers is depressed at the trailing side thereof.
 3. A heat exchanger including conduits for a heat exchanging fluid and corrugated heat exchanging fin elements secured to the conduits, each of said fin elements having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, each of said louvers being deformed at one of the leading and trailing sides thereof as viewed in the direction of feeding of a metal strip for the formation of the fin element so that the stress produced in the material of the louver is at least partially removed.
 4. A heat exchanger as defined in claim 3, wherein each of said louvers is depressed at the trailing side thereof.
 5. A method of manufacturing a corrugated heat exchanging fin element for use with a heat exchanger having conduits for a heat exchanging fluid, said fin element being adapted to be secured to the conduits, said fin element having formed thereon louvers extending therefrom at an angle with respect to the flow of a coolant and cut to define apertures opened in substantially the same direction, said method comprising the steps of feeding a metal strip into the nip of a pair of toothed roller dies having at least a row of louver forming blades formed on each of the teeth on the roller dies to cause the metal strip to be corrugated and formed with rows of louvers by said teeth and louver forming blades for forming an unfinished fin element, then feeding the latter into the nip of another pair of toothed rollers having at least a row of louver deforming portion on each of the teeth of the rollers to cause at one of the leading and trailing sides of each of the louvers to be deformed by said louver deforming portions whereby the stress produced in said trailing side of each louver at the time the same is formed is at least partially removed by the deformation.
 6. A method as defined in claim 5, wherein the trailing side of each of said louvers is depressed by said louver deforming portions on said another pair of rollers.
 7. A method as defined in claim 6, wherein, after the depression, the corrugated heat exchanging fin element is advanced into the nip of a further pair of toothed rollers by which said fin element is positively driven and advanced to a braking means which is in frictional sliding contact with the run of the fin element to narrow the pitch of the corrugation of the fin element by the brakiNg action of said braking means. 